Additional members of the complex of proteins that make up human growth hormone are to be studied. The components that have been characterized include the major 191-amino acid form, a 20,000-dalton variant and an inter-chain disulfide dimer. To be purified to homogeneity are 1) a form with a blocked amino terminus and 2) a slowly migrating form that has enhanced lactogenic activity. The substance will be studied chemically, physiologically and immunologically.